This application is based on Japanese Patent Application HEI 11-222730, filed on Aug. 5, 1999, all the contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a liquid crystal display and its manufacture method, and more particularly to an active matrix type liquid crystal display having a semiconductor active element such as a thin film transistor (TFT) for each pixel as a switching element.
b) Description of the Related Art
An active matrix type liquid crystal display has a plurality of scan lines extending in a row direction and a plurality of signal lines extending in a column direction. A pixel is disposed at each cross point of a matrix. Each pixel has a pixel electrode and a switching element connected to the pixel electrode. In the active matrix type liquid crystal display, pixel data is turned on and off by a switching element. Liquid crystal is used as display media.
As switching elements, a metal-insulator-metal (MIM) element and a three-electrode element, particularly a field effect thin film transistor having a gate, a source and a drain are used.
In this embodiment, a TFT connected to a pixel electrode is called a pixel TFT or simply TFT. A current terminal of the pixel TFT is called a drain, and a current terminal of TFT connected to the signal lines is called a source. A unit cell including a pixel electrode and TFT is called a pixel. An image is formed on a display area having a number of pixels disposed in a matrix shape.
A scan line disposed in the row direction is connected to the gate electrodes of TFTs of each row. A signal line disposed in the column direction is connected to the source electrodes of TFTs of each column.
A circuit for driving the scan lines is called a scan line driver, and a circuit for driving the signal lines is called a signal line driver. A circuit for driving a display area including the scan line driver and signal line driver is called a peripheral circuit.
An active matrix type liquid crystal display using as a switching element a TFT at each pixel electrode is more suitable for multiple pixels and provides a clearer image than a simple matrix type liquid crystal display having cross electrodes formed on a pair of substrates.
Most displays of personal computers, video camera view finders and the like use active matrix type liquid crystal displays.
In a conventional active matrix type liquid crystal display, signal lines and pixel electrodes (usually, transparent electrodes made of, for example, indium tin oxide (ITO)) are formed at the same layer level (usually on an interlayer insulating film), and a shading area called a black matrix (BM) is formed on the opposing substrate as a shading film for covering the space between adjacent pixel electrodes.
This structure requires some mask alignment margin between the pixel electrode and signal line and some substrate bonding margin for the pixel electrode and adjacent BMs. A ratio (called an opening ratio) of an effective pixel electrode area to the whole pixel electrode area becomes small. As pixels are made finer, the opening ratio becomes smaller.
The pixel electrode is formed in some cases at a layer level higher than the signal line (e.g., on a planarizing film formed on an interlayer insulating film). In this case, the pixel electrode area and the signal line area are formed overlapped to use the signal line itself as BM (TFT side BM). The mask alignment margin between the pixel electrode and signal line and the substrate bonding margin for the pixel electrode and adjacent BM can be made not so severe.
The structure using the TFT side BM requires two or more interlayer insulating films including the planarizing film. Therefore, back light is absorbed in the interlayer insulating films (particularly near the interface between the interlayer insulating films) and a bright display is difficult. A transmission factor lowers particularly on the low wavelength side.
It is an object of the present invention to provide a liquid crystal display providing a high image quality and a low power consumption.
According to one aspect of the present invention, there is provided a liquid crystal display having thin film transistors, an active matrix substrate, comprising: a first substrate; a plurality of scan lines formed on said first substrate and extending in the row direction; a plurality of first signal lines formed on said first substrate and intermittently extending in the column direction in an area excepting a cross area with said scan line and an area near the cross area; an interlayer insulating film covering said scan lines and said first signal lines; a plurality of first openings formed through said interlayer insulating film, said first openings exposing said first signal lines; and a plurality of second signal lines formed on said interlayer insulating film, said second signal lines being connected via said first openings to said first signal lines to form signal lines continuous in the column direction.
According to one aspect of the present invention, there is provided a liquid crystal display having an active matrix substrate, comprising: a first substrate; a plurality of island-shaped TFT polysilicon layers disposed in row and column directions on said first substrate in a matrix shape; a gate insulating film formed on said first substrate, said gate insulating film covering said polysilicon layers; a plurality of scan lines formed on said gate insulating film and extending in the row direction; a plurality of first signal lines formed on said gate insulating film and intermittently extending in the column direction in an area excepting a cross area with said scan line and an area near the cross area; an interlayer insulating film covering said scan lines and said first signal lines; a plurality of first openings formed through said interlayer insulating film, said first openings exposing said first signal lines; a plurality of second signal lines formed on said interlayer insulating film, said second signal lines being connected via said first openings to said first signal lines to form signal lines continuous in the column direction; pixel electrodes formed on said interlayer insulating film; and thin film transistors each disposed near the cross area between said scan line and said signal line, said thin film transistor including said TFT polysilicon layer as a channel layer, a gate electrode connected to said scan line, a source electrode connected to said signal line, and a drain electrode connected to said pixel electrode.
According to still another aspect of the present invention, there is provided a liquid crystal display having an active matrix substrate, comprising: a first substrate; a plurality of island-shaped TFT polysilicon layers disposed in row and column directions on said first substrate in a matrix shape; a gate insulating film formed on said first substrate, said gate insulating film covering said polysilicon layers; a plurality of scan lines formed on said gate insulating film, extending in the row direction, and crossing said polysilicon layers; a plurality of first signal lines formed on said gate insulating film and intermittently extending in the column direction in an area excepting a cross area with said scan line and an area near the cross area; an interlayer insulating film covering said scan lines and said first signal lines; a plurality of first openings formed through said interlayer insulating film, said first openings exposing said first signal lines; a plurality of second signal lines formed on said interlayer insulating film, said second signal lines being connected via said first openings to said first signal lines to form signal lines continuous in the column direction; pixel electrodes formed on said interlayer insulating film and having an extension portion in the column direction in each pixel area; a common electrode formed on said interlayer insulating film in an area adjacent to each of said pixel electrodes, said common electrode having a portion extending in an area of a plurality of pixels; and thin film transistors each disposed near the cross area between said scan line and said signal line, said thin film transistor including said TFT polysilicon layer as a channel layer, a gate electrode formed by said scan line or connected to said scan line, a source electrode connected to said signal line, and a drain electrode connected to said pixel electrode.
According to still another aspect of the present invention, there is provided a method of manufacturing a liquid crystal display having thin film transistors comprising the steps of: forming an electrode film on a first substrate; etching the electrode film to form a plurality of scan lines extending in a row direction above the first substrate, and a plurality of first signal lines intermittently extending in the column direction above the first substrate in an area excepting a cross area with said scan line and an area near the cross area; forming an interlayer insulating film over the first substrate; forming second signal lines on the interlayer insulating film, the second signal lines connecting the first signal lines via openings to form signal lines continuous in the column direction.
An active matrix type liquid crystal display having a high image quality and a bright image can be manufactured with simplified processes.
A manufacture yield and reliability can be improved.